By way of example, in the field of corrugated cardboard manufacture, it is customary to attach the strips of paper with glue. More precisely, a film of glue is deposited uniformly, in a given quantity, on one of the faces of these strips, and then the two strips are pressed and dried to form the band of cardboard.
In this connection, there are known .devices, such as wetting rolls, constituted by a cylinder immersed in a bath of the product to be applied. The main drawbacks of such devices reside in the difficulty of adjusting the quantity of product to be deposited, and in the fact that it is impossible to carry out partial treatments over a width less than that of the cylinder.
We also know spraying devices which enable the flow rate to be regulated via spray jets. However, in these devices, it is difficult to regulate the uniformity of the deposit provided. In addition, the use of pasty products is entirely out of the question.
Also known is a device for applying a liquid or pasty product on a continuously moving band, comprising means for depositing a film of liquid or pasty product on a surface of the band to be processed, as well as product feed means.
More precisely, the device comprises a product reservoir constituted by a sheet of flexible plastic, pressed over the moving band by means of a pressing blade, disposed across the band and forming the lower part of the reservoir.
To allow the product to be deposited on the moving band, the said plastic sheet has a rectangular window, the dimensions of which define the coating width and the quantity of product deposited.
Although this device gives satisfaction in certain cases, it is, however, unsuitable for high production rates, and its reliability depends on the tension applied to the band and on the quality of application of the window to the band.
As regards the coating of a band when only a portion of the width is coated, it receives a certain amount of humidity with the coating product, in particular in the form of an aqueous emulsion, it being necessary to moisten the non-processed portion with a thin film of water so that the moisture content of the band is fairly regular and homogeneous, to avoid, in particular, any phenomena of deformation liable to impair its flatness.
Now, given the high production rates of the devices used, which can, for example, represent as much as 300 m per minute of product coated over a width of 2 m 50, it is difficult to achieve swift adjustment of the manufacturing sequences, particularly when it is necessary to change coating products and/or modify the width of the band or bands to be coated. Now, in practice, such time consuming operations are prejudicial to the satisfactory operation of the device as several meters of cardboard thus travel past uncoated and have to be discarded, which leads to the production of waste through losses of material and increases manufacturing costs.
The object of the present invention is to provide a device for coating and/or impregnating with a liquid or pasty product a continuously moving band of material, which makes it possible to remedy the aforementioned drawbacks and which does not act as a curb on high production rates.
One of the objects of the present invention is to provide a coating and/or impregnating device that can be inserted into lines of machines for producing continuously moving bands of material and which is robustly and reliably constructed to enable it to operate at very high speeds of travel.
One of the objects of the present invention is to provide a device for coating and/or impregnating with a liquid or pasty product which makes it possible to control with accuracy the depositing of the said produce on the band of material travelling past, as well as its geometry, without it being necessary to modify the structure of the elements used.
Another object of the present invention is to provide a device for coating and/or impregnating with a liquid or pasty product which, thanks to its structure, permits easy control of its operation as well as automation of its settings.
Another object of the present is to provide a coating and/or impregnating device that does not slow down the manufacturing rates if, by reason of its adjustment, it is no longer in working position.
Another object of the present invention is to provide a coating and/or impregnating device that enables different products to be applied or deposited simultaneously or otherwise, thus increasing its working capabilities.
Another object of the present invention is to provide a coating and/or impregnating device that enables the cleaning fluids to be circulated and recovered in order to prevent pollution.
A further object of the present invention is to provide a coating and/or impregnating device which allows a better moisture content to be obtained over the whole of the band to be coated and/or impregnated while, at the same time, avoiding waste-generating losses of material.
Further objects and advantages of the present invention will become apparent in the course of the following description which is given, however, only by way of example, and is not intended to limit same.